Centrifuges are known to be provided with a rotary centrifuging drum rotating around a vertical axis and a scraper device comprising a fixed base, a tubular runner mounted on said fixed base such that it can rotate around and slide along a vertical central axis under the action of respective actuators, and a scraper assembly fixed at a lower end of the tubular runner and arranged, in a working position, for scraping a cylindrical inner surface of the rotary centrifuging drum. The scraper assembly generally includes one or more blades and one or more gas blow nozzles connected to a pressurized gas supply device.
In such scraper devices, it is also known that the tubular runner is configured as a plunger arranged inside a tubular jacket to form an integrated hydraulic cylinder coaxial with the central axis, and a stationary tubular rod is arranged inside the tubular runner and a gas conduit inside the tubular rod, the gas conduit having an upper end connected to a pressurized gas supply device and a lower end fixed to the tubular runner and in fluid communication with the one or more blow nozzles.
Nevertheless, this arrangement has some drawbacks. First, the gas conduit must be long enough so that its upper end is located outside the tubular rod even when the tubular runner is in a lower limit position, and as a result, when the tubular runner is in an upper limit position, a considerable section of the gas conduit projects from the upper end of the tubular rod, which increases the need for available space above the centrifuge. On the other hand, there is the risk that, in the event of an unexpected failure of the joint elements arranged between the plunger and the jacket, the oil actuating the hydraulic cylinder mixes with the gas expelled from the blow nozzles and contaminates the materials that are being centrifuged.
Patent document CN 103934126 A discloses a scraper device for centrifuge including a fixed base, a tubular runner which has a vertical central axis and is mounted on the fixed base by first guiding means allowing the tubular runner to rotate around and slide along the central axis, a scraper assembly fixed at a lower end of the tubular runner, a linear up and down actuator which has a longitudinal axis parallel to the central axis and is arranged on one side of the tubular runner and operatively connected for imparting to the tubular runner upward and downward movements along the central axis, and a rotation actuator operatively connected for rotating the tubular runner around the central axis. Nevertheless, this scraper device does not include a pressurized gas blowing device.
Patent document CN 202570422 U discloses a scraper device for centrifuge including a pressurized gas blowing device where a flexible gas conduit is wound around the tubular runner, the flexible gas conduit having an upper end connected to a pressurized gas supply device and a lower end fixed to the tubular runner and in fluid communication with one or more blow nozzles.